Post processing three-dimensional objects formed by selective deposition modeling

ABSTRACT

A method for removing supports from a three-dimensional objected formed by selective deposition modeling. The three-dimensional object is formed from a curable phase change material and the supports are formed from a non-curable phase change material. The curable phase change material contains between about 5% to about 25% of a non-reactive wax in order to achieve the desired phase change characteristics of the material. When removing the supports with heat, discoloration undesirably occurs in the three-dimensional object as the non-reactive wax migrates within the object. The method prevents wax migration by cooling the object slowly past the freezing point of the build material such that a temperature differential no greater than about 5° C. is present within the object. With the preferred build material having a freezing point of about 49.5° C., this is achieved by lowering the temperature between about 62° C. to about 52° C. over a period of between about 5 to about 10 minutes so that the temperature of the regions of the object remain substantially equal as the freezing point is crossed during cooling.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates in general to solid deposition modeling,and in particular to a post processing technique to remove a non-curablephase change support material from a three-dimensional object formedfrom a curable phase change build material.

[0003] 2. Description of the Prior Art

[0004] Recently, several new technologies have been developed for therapid creation of models, prototypes, and parts for limited runmanufacturing. These new technologies are generally called SolidFreeform Fabrication techniques, and are herein referred to as “SFF”.Some SFF techniques include stereolithography, selective depositionmodeling, laminated object manufacturing, selective phase areadeposition, multi-phase jet solidification, ballistic particlemanufacturing, fused deposition modeling, particle deposition, lasersintering, and the like. Generally in SFF techniques, complex parts areproduced from a modeling material in an additive fashion as opposed toconventional fabrication techniques, which are generally subtractive innature. For example, in most conventional fabrication techniquesmaterial is removed by machining operations or shaped in a die or moldto near net shape and then trimmed. In contrast, additive fabricationtechniques incrementally add portions of a build material to targetedlocations, layer by layer, in order to build a complex part. SFFtechnologies typically utilize a computer graphic representation of apart and a supply of a building material to fabricate the part insuccessive layers. SFF technologies have many advantages overconventional manufacturing methods. For instance, SFF technologiesdramatically shorten the time to develop prototype parts and can producelimited numbers of parts in rapid manufacturing processes. They alsoeliminate the need for complex tooling and machining associated withconventional subtractive manufacturing methods, including the need tocreate molds for custom applications. In addition, customized objectscan be directly produced from computer graphic data in SFF techniques.

[0005] Generally, in most SFF techniques, structures are formed in alayer by layer manner by solidifying or curing successive layers of abuild material. For example, in stereolithography a tightly focused beamof energy, typically in the ultraviolet radiation band, is scannedacross a layer of a liquid photopolymer resin to selectively cure theresin to form a structure. In Selective Deposition Modeling, hereinreferred to as “SDM” a phase change build material is jetted or droppedin discrete droplets, or extruded through a nozzle, to solidify oncontact with a build platform or previous layer of solidified materialin order to build up a three-dimensional object in a layerwise fashion.Other synonymous names for SDM used in this new industry are: solidobject imaging, solid object modeling, deposition modeling, multi-jetmodeling, three-dimensional printing, thermal stereolithography, and thelike. Often, a thermoplastic material having a low-melting point is usedas the solid modeling material, which is delivered through a jettingsystem such as an extruder or print head. One type of SDM process whichextrudes a thermoplastic material is described in, for example, U.S.Pat. No. 5,866,058 to Batchelder et al. One type of SDM processutilizing ink jet print heads is described in, for example, U.S. Pat.No. 5,555,176 to Menhennett et al. Some thermoplastic build materialsused in SDM are available and sold under the names Thermojet® 2000 andThermojet® 88 by 3D Systems, Inc. of Valencia, Calif. Also, someformulations for thermoplastic phase change build materials aredisclosed in U.S. Pat. No. 6,132,665 to Bui et al.

[0006] Recently, there has developed an interest in utilizing curablephase change materials in SDM. One of the first suggestions of using aradiation curable build material in SDM is found in U.S. Pat. No.5,136,515 to Helinski, wherein it is proposed to selectively dispense aUV curable build material in a SDM system. Some of the first UV curablematerial formulations proposed for use in SDM systems are found inAppendix A of International Patent Publication No. WO 97/11837, wherethree reactive material compositions are provided. More recent teachingsof using curable materials in three-dimensional printing is provided inU.S. Pat. No. 6,259,962 to Gothait and in International PublicationNumber WO 01/26023.

[0007] However, one of the most fundamental problems associated with SDMprocesses is the adverse effects resulting from gravitational forcesthat undesirably act on a part during the build process. All SDMprocesses must deal with gravitational forces. For example, mostdownward facing surfaces built by SDM processes need special supports inorder to stabilize the part during the build process.

[0008] One method of supporting the three-dimensional object to counterthe gravity problem is to utilize dissimilar materials in the buildprocess. For example, two different solidifying materials can beselectively deposited in a layer by layer process, one material forbuilding the part, and the other material for building the supportstructure. There are generally four recognized methods for removingdissimilar support material for an SDM object. Three of the methods wereinitially proposed in U.S. Pat. No. 5,136,515 to Helinski. The firstthree methods are 1) removing the support material by physical force, 2)removing the support material by application of heat, 3) removing thesupport material by chemical means. The forth method, having littleapplicability to SDM techniques, involves utilizing a powder as asupport material that does not adhere to the object.

[0009] In the first separation approach, the materials are carefullyselected to order to establish a weak bond joint at their juncture suchthat the application of an applied force separates the support structurefrom the part along the joint. For example, this approach is describedin U.S. Pat. No. 5,617,911 to Sterett et al and in InternationalPublication WO 01/26023 of Objet Geometries Ltd., in Rehovot, Israel.Undesirably, the application of applied force to crack or crumble awaythe support material from the object has limitations. For instance it isdifficult, and sometimes impossible, to remove the support material forcertain geometric configurations, such as in deep cavities or pockets.Further, delicate features of the three-dimensional object can be brokenor damaged during the removal process.

[0010] The second separation approach is to select a support materialhaving a lower melting point than the material of the formed object.After forming the object and support structure, the temperature of thecomposite is raised in order to melt out the support structure. Thistype of approach is described in, for example, U.S. Pat. No. 5,141,680to Almquist et al.

[0011] The third approach is to select a support material that issoluble in a solvent in which the build material is not. After formingthe object and support structure the two are submersed into the solventin order to dissolve away the support. One problem with this approach isthat as the solvent starts to saturate with removed support material,and eventually new solvent is needed. The disposal of the used solventcan be problematic. In addition, evaporative issues can arise resultingin the production of odors, and the like, when working with solvents.Thus, implementing this approach may not be user friendly or costeffective.

[0012] In the forth approach a removable support material is depositedin particulate form, such as a powder, that is energized so as to fuseto form the part, with the un-fused powder acting as the supportstructure. This type of approach is described in, for example, U.S. Pat.No. 5,252,264 to Forderhase et al. Undesirably, however, this 25approach is limited for use with sintered powder materials and isgenerally unsuitable in applications utilizing flowable solid modelingmaterials to build parts.

[0013] According to the present invention, a preferred build material isan acrylate/wax based curable phase change material, and a preferredsupport material is a wax based non-curable phase change material. Itwas initially envisioned to remove the support material by applicationof heat whereby the support material would melt away. However, initialpost processing tests utilizing heat to remove the support materialundesirably effected the three-dimensional object. The thermalprocessing apparently caused the otherwise transparent acrylate in theobject to become clouded and opaque. Further, the discoloration was notuniform throughout the object.

[0014] Thus, there is a need to develop a method and apparatus capableof removing a phase change support material dispensed to support athree-dimensional object formed from a curable phase change buildmaterial without undesirably effecting the three-dimensional object.These and other difficulties of the prior art have been overcomeaccording to the present invention.

BRIEF SUMMARY OF THE INVENTION

[0015] The present invention provides its benefits across a broadspectrum. While the description which follows hereinafter is meant to berepresentative of a number of such applications, it is not exhaustive.As will be understood, the basic methods and apparatus taught herein canbe readily adapted to many uses. It is intended that this specificationand the claims appended hereto be accorded a breadth in keeping with thescope and spirit of the invention being disclosed despite what mightappear to be limiting language imposed by the requirements of referringto the specific examples disclosed.

[0016] It is one aspect of the present invention to successfully removesupports formed from a phase change material from a three-dimensionalobject formed from a cured phase change material.

[0017] It is another aspect of the present invention to successfullyseparate supports from a three-dimensional object without undesirablyeffecting the underlying three-dimensional object.

[0018] It is a feature of the present invention that by the properapplication of heat the supports can be melted and removed from thethree-dimensional object without discoloring the object.

[0019] It is another feature of the present invention that after thesupport material has been melted and removed, that the temperature ofthe three-dimensional object is lowered to just above the freezing pointof the build material and then lowered below the freezing point at arate wherein a temperature differential within the regions of thethree-dimensional object does not exceed about 5° C.

[0020] It is an advantage of the present invention that the non-curablewax content in the build material is prevented from migrating within thematrix of build material of the three-dimensional object when postprocessing the object to remove the support material.

[0021] These and other aspects, features, and advantages areachieved/attained in the method of the present invention for postprocessing an article formed by selective deposition modeling, thearticle comprising a three-dimensional object and a support structure,the three-dimensional object formed from a curable phase changecomposition and the support structure formed from a non-curable phasechange composition. The post processing method comprises:

[0022] providing a temperature controllable environment for the articlehaving an initial temperature above the melting point of the non-curablephase change composition;

[0023] placing the article in the temperature controllable environment;

[0024] holding the temperature of the controllable environment above themelting point of the non-curable phase change composition untilsubstantially all of the support structure transitions to a flowablestate and is removed from the three-dimensional object;

[0025] lowering the temperature of the controllable environment to atemperature just above the freezing point of the curable phase changecomposition;

[0026] holding the temperature of the controllable environment justabove the freezing point of the curable phase change composition untilthe temperature of all the regions of the three-dimensional objectsubstantially equalize; and

[0027] lowering the temperature of the three-dimensional object belowthe freezing point of the curable phase change composition at a ratewherein a temperature differential within the regions of thethree-dimensional object does not exceed about 5° C.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The aspects, features, and advantages of the present inventionwill become apparent upon consideration of the following detaileddisclosure of the invention, especially when it is taken in conjunctionwith the accompanying drawings wherein:

[0029]FIG. 1 is a flow chart of the post processing method of thepresent invention.

[0030] To facilitate understanding, identical reference numerals havebeen used, where possible, to designate identical elements that arecommon in the FIGURE.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] While the present invention is applicable to all SDM techniquesand objects made therefrom, the invention will be described with respectto a SDM technique utilizing an ink jet print head dispensing aultraviolet radiation curable phase change material. However it is to beappreciated that the present invention can be implemented with any SDMtechnique utilizing a wide variety of curable phase change materials.For example, the curable phase change material can be cured by exposureto actinic radiation having wavelengths other than in the ultravioletband of the spectrum, or by subjecting the material to thermal heat.

[0032] As used herein, the term “a flowable state” of a build materialis a state wherein the material is unable to resist shear stresses thatare induced by a dispensing device, such as those induced by an ink jetprint head when dispensing the material, causing the material to move orflow. Preferably the flowable state of the build material is a liquidstate, however the flowable state of the build material may also exhibitthixotropic-like properties. A material is in a flowable state when thetemperature of the material is above the materials melting point. Theterm “solidified” and “solidifiable” as used herein refer to the phasechange characteristics of a material where the material transitions fromthe flowable state to a non-flowable state. A “non-flowable state” of abuild material is a state wherein the material is sufficientlyself-supportive under its own weight so as to hold its own shape. Abuild material existing in a solid state, a gel state, a paste state, ora thixotropic state, are examples of a non-flowable state of a buildmaterial for the purposes herein. A material is in a non-flowable statewhen the temperature of the material is below the materials freezingpoint. In addition, the term “cured” or “curable” refers to anypolymerization reaction. Preferably the polymerization reaction istriggered by exposure to actinic radiation or thermal heat. Mostpreferably the polymerization reaction involves the cross-linking ofmonomers and oligomers initiated by exposure to actinic radiation in theultraviolet or infrared wavelength band. Further, the term “cured state”refers to a material, or portion of a material, in which thepolymerization reaction has substantially completed. It is to beappreciated that as a general matter the material can easily transitionbetween the flowable and non-flowable state prior to being cured,however, once cured, the material cannot transition back to a flowablestate and be dispensed by the apparatus.

[0033] A preferred build material and support material is disclosed inthe concurrently filed U.S. patent application under docket numberUSA.269 entitled “Ultra-Violet Light Curable Hot Melt Composition”,which is herein incorporated by reference as set forth in full. Thematerials preferably have a melting point from about 45° C. to about 65°C., a freezing point from about 33° C. to about 60° C., and a jettingviscosity of about 10 to about 16 centipoise at the dispensingtemperature. A preferred method and apparatus for dispensing thepreferred materials to form a three-dimensional object and underlyingsupport structure is disclosed in the concurrently filed U.S. patentapplication filed under docket number USA.282 entitled “SelectiveDeposition Modeling with Curable Phase Change Materials”, which isherein incorporated by reference as set forth in full. The preferreddispensing temperature is about 80° C.

[0034] In general, both materials are dispensed in a layerwise mannerduring the SDM build process, and a planarizer is driven over each layerto normalize the layers during the build process. The build material isa photocurable acrylate/wax blend, and the support material is primarilya wax. After all the layers are formed it was envisioned that thesupport material could be easily and effectively removed by heating theobject and support structure above the melting point of the supportmaterial, causing the support material to melt away to reveal thethree-dimensional object.

[0035] Four formulations of the build material are provided by weightpercent in Table 1. The preferred build material is Example 4 in Table 1because it was determined to be the most durable. The materials had thefollowing physical properties as shown in Table 2. TABLE 1 GeneralComponent Mfg. ID No. Name Ex. 1 Ex. 2 Ex. 3 Ex. 4 CN980 UrethaneAcrylate 7.2% 6.5% CN981 Urethane Acrylate 26% E3200 Epoxy Acrylate 14%6.0% CN975 Hexafunctional 7.2% Urethane Acrylate CN2901 UrethaneAcrylate 27.5% 27% 18.7% Tetrahydrofurfuryl SR203 Methacrylate SR205Triethylene glycol 33% 46.5% 41.05% dimethacrylate SR340 2-phenoxyethylmethacrylate SR313 Lauryl methacrylate 18% Ethoxylated₃ SR454Trimethylolpropane 4.5% Triacrylate SR604 polypropylene glycol 12.0%monomethacrylate CD406 Cyclohexane 30% dimethanol diacrylate SR493DTridecyl Methacrylate 19% ADS038 Urethane wax 7% 5.3% 10% 10.0% ADS043Urethane wax 4.3% 6% 1.5% 2.0% I-184 Photo-initiator 2% 2% 2% 3.75%TOTAL 100% 100% 100% 100.0%

[0036] TABLE 2 Property Ex. 1 Ex. 2 Ex. 3 Ex. 4 Viscosity at 80° C. 12.9cps 12.9 cps 12.9 cps 12.8 cps Melting point ° C. 52° C. 55° C. 57° C.56° C. Freezing point ° C. 46° C. 47.5° C. 50° C. 49.5° C. Elongation %E 9% 4% 5% 11.3% (after cure)

[0037] The following components used in the four formulations listed inTable 1 are available from Sartomer Company, Inc. of Exton Pa. under thefollowing designations: CN 980, CN 981, CN 975, CN2901, SR 203, SR 205,SR 340, SR 313, SR 454, CD 406, SR604, and SR 493D. The components ADS038 and ADS 043 are available from American Dye Source, Inc. of Quebec,Canada. The epoxy acrylate under the designation E 3200 is availablefrom UCB Chemical, Inc. of Atlanta, Ga. The photoinitiator under thedesignation 1-184 listed is available from Ciba Specialty Chemicals,Inc. of New York, N.Y.

[0038] The formulations in Table 1 where made in accordance with thepresent invention by mixing the individual components in a kettleequipped with a mixing blade. A kettle was preheated to about 85° C. andthe components placed into the kettle, the kettle closed and stirringwas commenced. Stirring continued as the components eventually equalizedto the temperature of the kettle. Stirring was then continued until ahomogenized molten state was achieved. The viscosity was measured andadjusted as needed. It took approximately 2.5 hours to mix a 75-poundquantity of the formulations to a homogenized state. The build materialformulations were then removed from the kettle and filtered through a1-micron absolute filter while in the flowable state. The formulationswere then cooled to ambient temperature at which they transitioned fromthe flowable to the non-flowable state.

[0039] It is to be appreciated that about of the curable phase changebuild material formulations contain between about 5% to about 25% byweight of a non-reactive wax. In the preferred embodiment, thenon-reactive wax content is between about 10% to about 12% by weight,and is comprised of a urethane wax. However, other non-reactive waxescould be used such as carbon hydrogenated waxes, paraffin waxes, fattyester waxes, and the like. The wax content is necessary in order toprovide the appropriate phase change characteristics of the buildmaterial so that the material would solidify after being dispensed. Thiswax, which does not cure when exposed to actinic radiation, is trappedwithin the cured matrix of the polymerized reactive components of thebuild material formulation.

[0040] Because the materials are dispensed from the same dispensingdevice, the support materials have similar melting points, freezingpoints, and viscosity values at the dispensing temperature. Hence, thesupport material is formulated to have similar phase changecharacteristics as the curable phase change build material, andpreferably the characteristics are identical when possible. Thepreferred non-curable phase change support material comprises 70% byweight octadecanol available from Ruger Chemical Co., Inc., ofIrvington, N.J., and 30% by weight of a tackifier sold under thedesignation of KE 100 available from Arakawa Chemical (USA) Inc., ofChicago, Ill. This support material formulation has a viscosity of about11.0 centipoise at a temperature of about 80° C., and a melting point ofabout 58° C. and a freezing point of about 49.5° C. The formulation wasmixed in a kettle equipped with a mixing blade. The kettle is preheatedto about 85° C. and the octadecanol is placed into the kettle first, asit has the lower melting point. The kettle is closed and stirringcommenced. Once the octadecanol has melted, the KE 100 is added to themixture while stirring continues. The kettle is closed and stirringcontinues until a homogenized state of the mixture is achieved. Theviscosity is measured and adjusted if needed. The formulation is thenremoved from the kettle and filtered through a 1-micron absolute filterwhile in the flowable state. The formulation is then cooled to ambienttemperature wherein it transitions from the flowable to the non-flowablestate.

[0041] Test specimens were formed by an SDM apparatus utilizing thepiezoelectric Z850 print head used in the Phaser® 850 printer availablefrom Xerox Corporation's Office Products Business Unit of Wilsonville,Oreg. The Z850 print head was configured to also dispense a non-curablephase change support material as well as the curable phase change buildmaterial. The Z850 print head was modified to dispense the materials ata temperature of about 80° C. Both materials solidified generally uponcontact in the layer being formed during the build process, and aftereach layer was formed the layers were cured by exposure to actinicradiation. Only the reactive polymers in the dispensed build materialwere cured by the exposure to actinic radiation which initiated thepolymerization reaction. Hence, the test specimens comprised a matrix ofcured build material dispersed with between about 5% to about 25% byweight of a non-reactive wax, and the matrix being partially surroundedby solidified support material.

[0042] A variety of test specimens having different geometric shapeswere made. The test specimens needed to be generally representative ofthe variety of geometric shapes that can be made by SDM. Thin disks weremade that were about ⅛ inch thick having a diameter of about 2 inches.Thick disks were made that were between about 1 and 2 inches thickhaving a diameter of about 2 inches. A thin-walled 90-degree tubularelbow was also made for testing, as was a thin walled cell phone shellstructure.

[0043] The test specimens were used in order to develop an appropriatemethod for removing the support material. Generally it was preferred todevelop a method relying on thermal heat to bring the support materialback to a flowable state to melt the support material away and revealthe three-dimensional object. A number of methods were tried to providethermal heat to melt away the support material. Some of the first testsinvolved placing the test parts in a vat of organic oil at a temperatureof about 90° C. and allowing the support material to melt and settle tothe bottom of the vat. Peanut oil was used. The liquid vat was alsophysically agitated so as to assist in drawing the melted supportmaterial away from the three-dimensional object. In other tests mineraloil was also used as the heat transferring medium in the vat. In othertests the specimens were placed in an oven at a temperature of about 90°C. and the support material allowed to melt and run off the underlyingobjects and into container. Thus, organic oil, mineral oil, and air wereused as the heat transferring medium in many of the tests.

[0044] The initial post processing tests utilizing heat to remove thesupport material undesirably effected the three-dimensional object. Thetest specimens were initially placed in a temperature controlledenvironment between about 90° C. to about 200° C. to melt away thesupport material, and were then brought to room temperature within 5 to20 minutes. The thermal processing apparently caused the otherwisetransparent acrylate in the object to become clouded and opaque.Further, the discoloration was not uniform throughout the object. Thinfeatures appeared transparent and thick features appeared opaque. Avariety of different thermal processing steps were attempted to removethe supports, however internal discoloring of the three-dimensionalobject still occurred. It was not readily apparent what was causing theundesirable discoloration effect during post processing.

[0045] It was theorized that the discoloration occurs due to thermalstresses resulting during part cooling causing the wax content thatpermeates the matrix of cured build material to migrate to regions oflower compressive stresses during post processing. The liquid wax isbelieved to move in capillary like fashion towards regions of the partwhich remain above the freezing point of the build material composition.As the part cools rapidly below the freezing point, generally belowabout 70° C., the external regions cool before the internal regions ofthe part. As the outer regions cool and contract faster than the innerregions, the wax component in the build material is believed to migratetowards the inner regions of the three-dimensional object, and the innerportions then solidify with a substantially higher volume percentage ofthe wax component. It is believed that this produces objects undesirablyhaving transparent edges and opaque centers. It is believed thetransparent edges of the objects are where the wax content had migratedfrom, and the opaque centers of the objects are where the wax contenthad migrated to.

[0046] It was then proposed that by cooling the part slowly and evenlyafter the support material has been substantially melted and removed,the wax component in the build material would be prevented from becomingtransient. It was believed this would eliminate the undesirablediscoloration effects. Test specimens were placed in a temperaturecontrolled vat of oil. The temperature of the vat was initially raisedto between about 90° C. and about 150° C. prior to placing the specimensin the vat. The support material melted and settled to the bottom of thevat. The temperature in the vat was then controllably lowered to roomtemperature very slowly so that the temperature of the regions of thespecimens would remain substantially equal and not vary by more than 5°C. at any point in time. The specimens processed in this manner did notexhibit any of the undesirable discoloring effects previously shown.Thus, it was determined that by keeping the temperature differential ofthe regions within the three-dimensional object between less than about5° C. at any point in time during the cooling process, the undesirablediscoloring effects are eliminated. Alternatively stated, if thetemperature of the regions of the three-dimensional object remainsubstantially equal during the cooling process, the undesirablediscoloring effects are eliminated. However, it is undesirable tomaintain this temperature differential during the entire cooling processas the process would take too long, particularly for largethree-dimensional objects.

[0047] It was then proposed that the 5° C. temperature differential needonly be maintained when cooling the specimens past the freezing point ofthe build material. This was investigated by placing specimens in atemperature controlled environment comprising a heated vat of oil. Thetemperature of the vat was initially raised to between about 90° C. andabout 150° C. prior to placing the specimens in the vat. After thespecimens were placed in the vat the support material melted and settledto the bottom. The temperature of the vat was then lowered to about 75°C. The temperature in the vat was then controllably lowered betweenabout 75° C. to about 40° C. so that the temperature of the regions ofthe specimens would remain substantially equal as the freezing point ofthe build material composition was crossed. After the freezing point wascrossed, most of the specimens were removed from the vat and allowed toreturn to ambient temperature. It was determined from further testingthat cooling the specimens from between about 65° C. to about 45° C.over a period of between about 5 to about 10 minutes eliminated thediscoloration effects discussed previously, in which the freezing pointof the build material composition was within this temperature range,such as the preferred build material in example 4 of Table 1 which has afreezing point of about 49.5° C. Thus, it was discovered that loweringthe temperature between about 65° C. to about 45° C. over a period ofbetween about 5 to about 10 minutes allows the temperature of theregions of the specimens to remains substantially equal as the freezingpoint is crossed during the cooling.

[0048] It was also found that initial melting temperatures generallyabove about 150° C. caused the cured components in the objects to crackand/or delaminate. Some specimens heated above about 150° C. give theappearance of having trapped bubbles, and some turned yellow. Thus, itwas determined the initial temperature for removing the support materialshould not be raised above about 150° C. It was further found that thesupport material could be effectively removed from the three-dimensionalobjects at temperatures between about 90° C. and about 150° C., andpreferably between about 120° C. and about 125° C.

[0049] Further experimentation was conducted with mineral oil as theliquid heat transferring medium in the vat instead of organic oil.Mineral oil as the heat transferring medium also provided successfulresults. When using organic oil such as peanut oil, slight yellowing wasdetected on the resultant objects, however no yellowing was present whenusing mineral oil. If desired, other liquid mediums could be used aswell, such as water. If water is used, the support material can easilybe removed from the water, as it will float on the top surface of thewater. When using water, the initial temperature should generally notexceed about 100° C., however coolant additives such as ethylene glycolcan be included to prevent boiling at higher temperatures. Petroleumdistillate based oils were also tried as a means for removing thesupport material with the hopes that the oil would help dissolve the waxmaterial in the support material. The support material did melt, howeverthe distillate penetrated the build material and appeared to dissolveand remove the constituent wax component of the build material. Thisleft a bright white part without any transparency.

[0050] It is to be appreciated that there are a variety of ways toprovide a temperature controllable environment for the post processingsteps of the present invention. Instead of providing a liquid heattransferring medium in a vat, an oven operated in air can be used.Further, some of the steps can be executed with one temperaturecontrollable device utilizing one heat transferring medium and othersteps executed by a different temperature controllable device utilizinga different heat transferring medium. For instance, an oven can be usedto initially remove a substantial amount of the support material, andthe object can then be placed in a liquid vat for removing any residualsupport material. In this case a catch tank can acquire the substantialamount of support material removed by the oven, thereby reducing thequantity residing in the liquid vat. Because the support material in theliquid vat at some point must be removed, it is desirable to minimizethe quantity of support material in the vat of liquid as much aspossible. Alternatively, a vat of liquid support material can beprovided for initially removing the support material instead of an oven.This would be advantageous as the non-curable phase change supportmaterial composition in a flowable state can be the heat transferringmedium, and the material can be recycled without the need to separatethe material from some dissimilar liquid heat transferring medium suchas water or oil.

[0051] Other heat transferring mediums can be used as well. Forinstance, a bed of particles can be used, in which capillary action ofthe particles can assist in the removal of support material. If desired,a fluidized bed of particles can be used. The particles can be any solidcomposition of matter that does not melt when subjected to temperaturesof about 150° C. For example, nearly any metal, mineral, ceramic, orcombination thereof, could be used as the particulate matter. However tosubmerse an article in a particulate bed may require the assistance ofagitation and vibration. If needed, such assistance must be sufficientlygentle such that delicate features of the underlying three-dimensionalobject are not damaged.

[0052] Referring to FIG. 1, the post processing procedure of the presentinvention is generally identified by numeral 10. The post processingprocedure 10 involves providing a temperature controllable environmentfor the article at an initial temperature 12, followed by placing thearticle in the temperature controllable environment 14. The initialtemperature is above the melting temperature of the support material soas to cause it to transition to a flowable state. The next stepidentified by numeral 16 involves holding the temperature of thecontrollable environment above the melting point of the phase changesupport structure until substantially all of the support material of thearticle is removed from the three-dimensional object. The next stepidentified by numeral 18 involves lowering the temperature of thethree-dimensional object to a temperature just above the freezing pointof the build material composition. The temperature just above thefreezing point should be no more than about 15° C. above the freezingpoint so that the post processing will not take too long. The next stepidentified by numeral 20 involves holding this temperature until thetemperature of all the regions of the three-dimensional objectsubstantially equalize. Generally about 20 minutes is needed for thetemperature of the three-dimensional object to equalize throughout allregions of the object. The final step identified by numeral 22 involvesslowly lowering the temperature of the three-dimensional object belowthe freezing point of the build material composition while keeping thetemperature of the regions of the three-dimensional object substantiallyequal as the freezing point is crossed during the cooling step.Preferably the rate at which the temperature is lowered is sufficientlygradual such that a temperature differential within thethree-dimensional object does not exceed about 5° C. at any time duringcooling, and particularly when crossing the freezing point of the buildmaterial. Preferably the freezing point is crossed by about 5° C. belowthe freezing point, at which the three-dimensional object can bereturned to ambient conditions at about any desired rate.

[0053] The use of hot organic based oils produced several advantagesover other heating transferring mediums. For example, the peanut oilused in the experiments has a slightly lower density than cured materialforming the specimens. This small density difference allows the part toremain submerged and nearly weightless during heating while alsoproviding a means for transporting the melted material away from thepart, as it will sink to the bottom of the vat. At about 120° C. the hotoil is reasonably safe to touch, and the entire post processing steps toremove the support material can be completed in under an hour. Inaddition, these organic oils, such as vegetable oil, peanut oil,sunflower oil, and the like, are non-toxic.

[0054] A preferred method of post processing an article formed by SDMinitially comprises providing a temperature controllable environmentcomprising an oven with the heat transferring medium being air. Thetemperature of the oven is initially raised above the melting point ofthe phase change support structure, and the article is then placed inthe oven. Preferably the temperature is between about 80° C. and about150° C., and more preferably to between about 120° C. to about 125° C.At this temperature the phase change support structure melts. Thetemperature is maintained for about 20 minutes so that substantially allof the support material is removed from the underlying three-dimensionalobject. The support material is drained into a container for disposal orrecycling. This is done to remove a substantial amount of the supportmaterial prior to placing the three-dimensional object in a liquid heattransferring medium to remove the residual material. This substantiallyreduces the quantity of support material that must later be removed fromthe liquid.

[0055] The three-dimensional object is then submersed in a vat of liquidat a temperature of between about 80° C. and about 150° C. Preferablythe liquid is mineral oil, although other liquids could be used, such asorganic oil or water. The vat is held at this temperature for about 20minutes as the mineral oil is continuously stirred so as to remove theresidual support material from the object. Preferably the temperature ofthe mineral oil is near the temperature at which the bulk of supportmaterial was removed in the oven. Stirring is accomplished with a paddlewheel provided within the container of mineral oil that is rotablydriven at a constant angular velocity. While the mineral oil iscontinuously stirred, the residual support material settles to thebottom of the vat.

[0056] Next the temperature of the three-dimensional object is loweredto a temperature just above the freezing point of the build materialcomposition, such as about 75° C., and held there for about 20 minutes.For the preferred build material, the temperature is lowered to aboveabout 62° C., and is held there for about 20 minutes. Holding thetemperature for about 20 minutes allows all the temperature of all theregions of the three-dimensional object to substantially equalize. Thetemperature is then slowly lowered below the freezing point temperatureof the build material composition, such as to about 40° C. Lowering thetemperature between about 75° C. to about 40° C. over a period ofbetween about 15 minutes allows the temperature of the regions of thethree-dimensional object to remain substantially equal as the freezingpoint is crossed during the cooling process. For the preferred buildmaterial, the temperature is lowered between about 62° C. to about 52°C. over a period of between about 10 minutes. Afterwards, thetemperature of the three-dimensional object is returned to roomtemperature. Preferably the object is removed from the mineral oil andallowed to air dry.

[0057] The final step is a soapy water rinse with a liquid detergent ata temperature between 20° C. to about 50° C. This allows for the removalof any residual mineral oil and particles of support material from thesurface of the object. A preferred liquid dishwashing detergent used isDAWN® liquid dish detergent available from Procter & Gamble ofCincinnati, Ohio. Preferably the steps are automated and performed by asingle post processing apparatus. After the soapy water rinse thethree-dimensional object is then air dried and cooled to atmosphericconditions.

[0058] What has been described are preferred embodiments in whichmodifications and changes may be made without departing from the spiritand scope of the accompanying claims.

What is claimed is:
 1. A method of post processing an article formed byselective deposition modeling to remove a support structure, the articlecomprising a three-dimensional object and the support structure, thethree-dimensional object formed from a curable phase change compositionand the support structure formed from a non-curable phase changecomposition, the method comprising the following steps: (a) providing atemperature controllable environment for the article having an initialtemperature above the melting point of the non-curable phase changecomposition; (b) placing the article in the temperature controllableenvironment; (c) holding the temperature of the controllable environmentabove the melting point of the non-curable phase change compositionuntil substantially all of the support structure transitions to aflowable state and is removed from the three-dimensional object; (d)lowering the temperature of the controllable environment to atemperature just above the freezing point of the curable phase changecomposition; (e) holding the temperature of the controllable environmentjust above the freezing point of the curable phase change compositionuntil the temperature of all the regions of the three-dimensional objectsubstantially equalize; and (f) lowering the temperature of thethree-dimensional object below the freezing point of the curable phasechange composition at a rate wherein a temperature differential withinthe regions of the three-dimensional object does not exceed about 5° C.2. The method of claim 1 wherein the temperature controllableenvironment includes at least one heat transferring medium.
 3. Themethod of claim 2 wherein the heat transferring medium is air.
 4. Themethod of claim 2 wherein the heat transferring medium is a solid. 5.The method of claim 4 wherein the solid heat transferring mediumcomprises a plurality of particulate matter.
 6. The method of claim 2wherein the heat transferring medium is a liquid.
 7. The method of claim6 wherein the liquid is an organic oil, a mineral oil, water, or thenon-curable phase change composition in a flowable state.
 8. The methodof claim 2 wherein steps (a) (b) and (c) are completed in a heattransferring medium of air, and the steps (d) (e) and (f) are completedin a liquid heat transferring medium.
 9. The method of claim 1 whereinthe initial temperature of the controllable environment is between about90° C. to about 150° C.
 10. The method of claim 1 wherein the initialtemperature of the controllable environment is between about 120° C. toabout 125° C.
 11. The method of claim 1 wherein the step of holding thetemperature of the controllable environment above the melting point isaccomplished for a time period of at least about 20 minutes.
 12. Themethod of claim 1 wherein the step of lowering the temperature of thecontrollable environment to just above the freezing point is betweenabout 75° C. to about 65° C.
 13. The method of claim 1 wherein the stepof holding the temperature of the controllable environment just abovethe freezing point is accomplished for a time period of at least about20 minutes.
 14. The method of claim 1 wherein the step of lowering thetemperature of the three-dimensional object below the freezing point isaccomplished through a temperature range of between about 75° C. toabout 40° C.
 15. The method of claim 1 wherein the step of lowering thetemperature of the three-dimensional object below the freezing point isaccomplished through a temperature range of between about 62° C. toabout 52° C. for a period of time between about 5 minutes to about 10minutes.
 16. A method of post processing an article formed by selectivedeposition modeling, the article comprising a three-dimensional objectand a support structure, the three-dimensional object formed from acurable phase change composition and the support structure formed from anon-curable phase change composition, the method comprising thefollowing steps: (a) providing a temperature controllable environmentfor the article having an initial temperature above the melting point ofthe non-curable phase change composition; (b) placing the article in thetemperature controllable environment; (c) holding the temperature of thecontrollable environment above the melting point of the non-curablephase change composition until substantially all of the supportstructure transitions to a flowable state and is removed from thethree-dimensional object; (d) lowering the temperature of thecontrollable environment to a temperature just above the freezing pointof the curable phase change composition; (e) holding the temperature ofthe controllable environment just above the freezing point of thecurable phase change composition until the temperature of all theregions of the three-dimensional object substantially equalize; and (f)lowering the temperature of the three-dimensional object below thefreezing point of the curable phase change composition at a rate whereinthe temperature of the regions of the three-dimensional object remainsubstantially equal as the freezing point is crossed.
 17. The method ofclaim 16 wherein the temperature controllable environment includes atleast one heat transferring medium.
 18. The method of claim 17 whereinthe heat transferring medium is air.
 19. The method of claim 17 whereinthe heat transferring medium is a solid.
 20. The method of claim 19wherein the solid heat transferring medium comprises a plurality ofparticulate matter.
 21. The method of claim 17 wherein the heattransferring medium is a liquid.
 22. The method of claim 17 wherein theliquid is an organic oil, a mineral oil, water, or the non-curable phasechange composition in a flowable state.
 23. The method of claim 16wherein steps (a) (b) and (c) are completed in a heat transferringmedium of air, and the steps (d) (e) and (f) are completed in a liquidheat transferring medium.
 24. The method of claim 16 wherein the initialtemperature of the controllable environment is between about 90° C. toabout 150° C.
 25. The method of claim 16 wherein the initial temperatureof the controllable environment is between about 120° C. to about 125°C.
 26. The method of claim 16 wherein the step of holding thetemperature of the controllable environment above the melting point isaccomplished for a time period of at least about 20 minutes.
 27. Themethod of claim 16 wherein the step of lowering the temperature of thecontrollable environment to just above the freezing point is betweenabout 75° C. to about 65° C.
 28. The method of claim 16 wherein the stepof holding the temperature of the controllable environment just abovethe freezing point is accomplished for a time period of at least about20 minutes.
 29. The method of claim 16 wherein the step of lowering thetemperature of the three-dimensional object below the freezing point isaccomplished through a temperature range of between about 75° C. toabout 40° C.
 30. The method of claim 16 wherein the step of lowering thetemperature of the three-dimensional object below the freezing point isaccomplished through a temperature range of between about 62° C. toabout 52° C. for a period of time between about 5 minutes to about 10minutes.
 31. A method of post processing an article formed by selectivedeposition modeling to remove a support structure, the articlecomprising a three-dimensional object and the support structure, thethree-dimensional object formed from a curable phase change compositionand the support structure formed from a non-curable phase changecomposition, the method comprising the following steps: (a) providing atemperature controllable environment for the article having an initialtemperature above the melting point of the non-curable phase changecomposition; (b) placing the article in the temperature controllableenvironment; (c) removing substantially all of the support structure ina flowable state from the article; (d) lowering the temperature of thecontrollable environment to a temperature just above the freezing pointof the curable phase change composition and allowing the temperature ofall the regions of the three-dimensional object to substantiallyequalize; (e) lowering the temperature of the three-dimensional objectbelow the freezing point of the curable phase change composition at arate wherein a temperature differential within the regions of thethree-dimensional object does not exceed about 5° C.
 32. The method ofclaim 31 wherein the temperature controllable environment includes atleast one heat transferring medium.
 33. The method of claim 32 whereinthe heat transferring medium is air.
 34. The method of claim 32 whereinthe heat transferring medium is a solid.
 35. The method of claim 34wherein the solid heat transferring medium comprises a plurality ofparticulate matter.
 36. The method of claim 32 wherein the heattransferring medium is a liquid.
 37. The method of claim 36 wherein theliquid is an organic oil, a mineral oil, water, or the non-curable phasechange composition in a flowable state.
 38. The method of claim 32wherein steps (a) (b) and (c) are completed in a heat transferringmedium of air, and the steps (d) and (e) are completed in a liquid heattransferring medium.
 39. The method of claim 31 wherein the step oflowering the temperature of the controllable environment to just abovethe freezing point is between about 75° C. to about 65° C.
 40. Themethod of claim 31 wherein the step of lowering the temperature of thethree-dimensional object below the freezing point is accomplishedthrough a temperature range of between about 75° C. to about 40° C. 41.The method of claim 31 wherein the step of lowering the temperature ofthe three-dimensional object below the freezing point is accomplishedthrough a temperature range of between about 62° C. to about 52° C. fora period of time between about 5 minutes to about 10 minutes.